Advanced wireless communications products demand integrated circuit technologies with high performance, high levels of system integration, low power and low cost. For wireless applications up to several GHz silicon bicmos technology is uniquely suited to meet these requirements. Of critical important to RF design is the availability of high quality passive components. In particular, it is desirable to have implanted thin film resistors that have a low temperature coefficient of resistance (TCRL). Unfortunately, existing techniques for polysilicon thin film resistors generally result in thin film resistors with relatively large temperature coefficients of resistance. We have discovered a process and a low temperature coefficient resistor that overcomes the problem of the prior art.
We have discovered a polysilicon thin film low temperature coefficient resistor and a method for making the same. The TCRL is formed on a layer of insulation, typically silicon dioxide or silicon nitride. The layer comprises polysilicon that has a relatively high dopant concentration and has a substantial amount of unannealed implant damage. The polysilicon is implanted with one or more species. However, contrary to prior art methods, the implanted resistor is annealed less than typical prior art implanted resistors in order to leave some unannealed damage in the resistor. This gives the TCRL a higher resistance without increasing its temperature coefficient. Thus, even though the temperature may increase, the relative value of the resistance remains the same. As such, the resistor is more precise and may be used in connection with the precision requirements for high quality RF devices.